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This medium was devised by Handford (1974). It depends upon (i) the selective inhibitory properties of oleandomycin, polymyxin and sulfadiazine and (ii) an indicator system involving sulfite and ferric iron. Most unwanted organisms are suppressed while Clostridium perfringens and related species will reduce the sulfite and form black colonies due to the production of ferrous sulfide (Mead et al., 1982).

Suspend ingredients other than the oleandomycin and polymyxin in 1 L of water. Bring to the boil to dissolve completely. Dispense 100 mL amounts into bottles (or final containers) and sterilise at 121°C for 15 min. Concentrated stock solutions of the antibiotics are made by dissolving 0.5 g of oleandomycin phosphate in 100 mL of sterile distilled water and by dissolving 500 000 i.u. of polymyxin B sulfate in 5 mL of sterile distilled water. These concentrated solutions are further diluted 1 in 100 and, just before pouring, 1 mL of each diluted solution is added to the molten basal medium.